1) Field of the Invention
Embodiments of the present invention relate to a structural assessment and monitoring system and, more particularly, to a passive structural assessment and monitoring system for inspecting a structure.
2) Description of Related Art
Non-destructive inspection (NDI) of structures involves thoroughly examining a structure without harming the structure or requiring its significant disassembly. Non-destructive inspection is typically preferred to avoid the schedule, labor, and costs associated with removal of a part for inspection, as well as avoidance of the potential for inducing damage into the structure. Non-destructive inspection is advantageous for many applications in which a thorough inspection of the exterior and/or interior of a structure is required. For example, non-destructive inspection is commonly used in the aircraft industry to inspect aircraft structures for any type of internal or external damage to or defects (flaws) in the structure. Inspection may be performed during manufacturing or after the completed structure has been put into service, including field testing, to validate the integrity and fitness of the structure. In the field, access to interior surfaces of the structure is often restricted, requiring disassembly of the structure, introducing additional flow time and labor costs.
Among the structures that are routinely non-destructively tested are composite structures, such as composite sandwich structures and other adhesive bonded panels and assemblies and structures with contoured surfaces. These composite structures, and a shift toward lightweight composite and bonded materials such as using graphite materials, dictate that devices and processes are available to ensure structural integrity, production quality, and life-cycle support for safe and reliable use. As such, it is frequently desirable to inspect structures to identify any defects, such as cracks, discontinuities, voids, or porosity, which could adversely affect the performance of the structure. For example, typical defects in composite sandwich structures, generally made of one or more layers of lightweight honeycomb or foam core material with composite or metal skins bonded to each side of the core, include disbonds which occur at the interfaces between the core and the skin or between the core and a buried septum.
Various types of sensors may be used to perform non-destructive inspection. One or more sensors may move over the portion of the structure to be examined, and receive data regarding the structure. For example, a pulse-echo (PE), through transmission (TT), or shear wave sensor may be used to obtain ultrasonic data, such as for thickness gauging, detection of laminar defects and porosity, and/or crack detection in the structure. Resonance, pulse-echo, or mechanical impedance sensors are typically used to provide indications of voids or porosity, such as in adhesive bondlines of the structure.
High resolution inspection of aircraft structure is commonly performed using ultrasonic testing (UT) to provide a plan view image of the part or structure under inspection. Data acquired by sensors is typically processed and then presented to a user via a display as an image of the inspected structure. To increase the rate at which the inspection of a structure is conducted, a scanning system may include arrays of inspection sensors, i.e., arrays of transmitters and/or detectors. Non-destructive inspection may be performed manually by technicians who typically move an appropriate sensor over the structure, by semi-automated inspection systems (e.g., the Mobile Automated Scanner (MAUS®) system), and by automated inspection systems (e.g., Automated Ultrasonic Scanning System (AUSS®) system) that have also been developed.
New aircraft structures comprised of composites, multi-functional systems, and complex geometries create a maintenance burden for aircraft inspection. The maintenance tools, procedures, and practices used on metallic aircraft are generally not compatible or cost effective with next generation aircraft structures. New aircraft structures will most likely be a mix of bonded and bolted laminates with a variety of metallic and composite substructures. Removing panels to gain access to structural components will be more difficult with these new integrated structural systems.
Since composite materials can often hide a defect, a detection system is needed to promote user confidence and to reduce the impact of additional undetected damage growth. The ability to detect flaws, monitor anomalies, or predict damage is dependant on the system and sensors used by inspectors. Using existing NDI equipment and processes presents a solution that is costly and time-consuming. In particular, for in-service inspection, NDI sensors are generally placed by hand onto the structure under inspection by an inspector, who is unable to easily access all locations that require inspection. Inspection of some areas of an aircraft can be time-consuming and costly because of their locations.
It would therefore be advantageous to provide a system that is capable of monitoring and assessing a structure. In addition, it would be advantageous to provide a system that is capable of inspecting structures effectively and efficiently. Furthermore, it would be advantageous to provide a system that is economical to manufacture and use.